Internal combustion engine



April 5, 1938. H. c. COLBURN 2,112,829

INTERNAL COMBUSTION ENG INEF Filed Aug. 7, 1955 4 Sheets-Sheet 1 34 I I I W W Invenlvr jfrberllfflolburn.

April 1938- H. c. COLBURN INTERNAL COMBUSTION ENGINE Filed Aug. 7, 1935 4 Sheets-Sheet 2 I nverzlar erberlCtolburfl.

llll lllll L llllllllll P 5, 1933- H. c. COLBURN INTERNAL COMUSTION ENGINE Filed Aug. 7, 1935 4 Sheets-Sheet 3 April 5, 1938.

H. C. COLBURN INTERNAL COMBUSTION ENGINE Filed Aug. 7, 1935 4 SheetsSheet 4 llntented Apr. ,193 v i ;,z, zg J UNITED STATES PATENT .oFFicE INTERNAL COMBUSTION nin'cnm Herbert G. Colburn, South Pasadena, Calif., al-

signor to Colburn Engineering Corporation, Santa Monica, Calif., a corporation of Colorado Application August 7, 1935, Serial No. 35,124

5 Claims. (01. 123-51) This invention relates generally and typically this specific engine of the prior art, that causes to internal combustion engines of the type in the exhaust controlling piston to move in advance which two opposed pistons move oppositely in a of the intake controlling piston, so that the excylinder, the heads of the pistons defining an haust port is uncovered before the intake port 5 intermediate combustion chamber, and in which is uncovered, and also is covered before the intake connecting rods extend outwardly from the pisport is covered. However, an engine utilizing tons to connect with suitable linkage driving the this specific linkage has an inherent practical crank shaft. Such an engine may advantalimitation, in that the extent of such advance of geously be of the two cycle type, and the present the exhaust piston depends upon the vertical disinvention, in certain of its aspects, deals espetance of the crank. shaft above the tangential 10 cially with the two cycle type of engine. The line drawn between the arcs described by the present application is a continuation in part of lower pivotal connections of the rock levers, and my copending application entitled Internal to accomplish such an advance as is necessary for combustion engine, filed March 2, 1931, Serial a practical high speed engine, the crank shaft 15 No. 519,297, wherein was disclosed an engine emwould have to be raised sohigh above said line 15 bodying certain of the features claimed in the that it would intersect or interfere with the present application. working cylinder, or its water jacket.

When an engine of the type mentioned is de- It is accordingly an object of the present invensigned for two cycle operation, the cylinder is 'tion to provide an engine of the type herein de- 0 provided with an intake port near the outer limit scribed with an improved linkage arrangement of movement of one piston and with an exhaust between the pistons and crank shaft by which port near the outer limit of movement of the the advance of the exhaust piston over the inother piston. When these pistons are at the outtake piston may be substantially increased over er limits of their strokes, both ports are unwhat is possible with linkages heretofore known.

5 covered and exhaust gases escape by the exhaust A further object of the invention is to provide port while fresh or carbureted air enters by the a linkage in which maximum turning effort is intake port. It is highly desirable in such an received at the crank, and in which the leverage engine that the exhaust port be uncovered prior relations between the rock levers, connecting rods to opening of the intake port, and then be closed and crank shaft are substantially improved.

39 before the intake port is closed. -This sequence A further object of the invention is to provide of events has the dual advantage that the flame an. improved engine of the type involving two within the cylinder may escape through the expairs of opposed pistons working in cylinders haust port before the fresh charge is admitted disposed on opposite sides of a transversely exthrough the intake port, thus obviating possitending crank shaft, and to provide improved as bllity of igniting the fresh charge and backfiring means of operative connection between the pisthrough the intake manifold, and also that the tons and the crank shaft. fresh charge, which is still entering the cylin- In accordance with the present invention, the der after the exhaust port has been closed, crank shaft is offset below, rather than above, may be compressed through use of a super- 9. line drawn tangentially to the arcs described charger toapressure above atmospheric. Alinkby the lower pivotal connection of the rock 40 age capable of performing this sequence of events levers. I have found that such a crank shaft has previously been known, and consists (assumposition also causes one piston to move in ading the cylinder to be horizontally disposed) of vance of the other, and at the same time has the a pair of rocking levers, one at each end of the notable advantage that the exhaust piston can cylinder, each such lever being connected at its be designed to move substantially further in ad- 45 upper end to one of the pistons in the cylinder, vance of the intake piston than is possible when and rods connected between the lower ends of the crank shaft is offset in an upward direction. said rocking levers and the crank shaft, which It may readily be demonstrated that the greater extends below and at right angles to the axis the offset of the crank shaft from the tangential .,0 of the cylinder, the axis of the crank shaft being line in question, the greater is the advance of the located above a line tangential to the arcs deone piston over the other. An advantage of scribed by the pivotal connections between the great importance in placing the crank shaft belower extremities of the rock levers and the low rather than above this line arises from the aforementioned rods. It is the placement of the fact that there is no immediate mechanical crank shaft axis above this tangential line, in limitation on the distance the crank shaft, may. y

crank shaft, as compared with an upwardly offing partial escape the exhaust gases at low set crank shaft, arisesfrom improved leverage relations between the rock levers and the crank,-

it being found that the downwardly oifset crank shaft results in the .crank effort increasing somewhatmore rapidly as the-pistons move outwardly from inward dead center.

A still further advantage in offset crank shaft arrangement arises when-the engine is built in two cylinder for|n,-'witholie.v cylinder placed on each side of the crank shaft.

The downwardly, or inwardly, offset draft gineis so adjusted that at the chargeofalriustreachestheexhaustportatthe time'said port closes, then :the fresh charge may not reach the exhaust port in time to elect complete scavenging at high speed; if scavenging at high speed is fresh charge may reach partly. through the exhaust port before the exhaust port closes when'the engine is operating at low speed. Usually, the engine is designed substantially complete scavenging at high speed. with the result that a part of the fresh charge escapes with the exhaust gases at each stroke when the engine is operating at low speed. In this way, a two cycle engine is often much more uneconomical of fuel at low speed than at high speed. f

It is a further primary obiectof the present invention to provide a control-means by which at all engine speeds the fresh charge completelyv scavenges the cylinder, without partially escaping with the exhaust gases.

In accordance with the preferred embodiment of the present invention, a supercharger is used of a positive displacement type, supplying a constant quantity of air per engine stroke for a given setting of the throttle. A variable opening shutter means is provided at. the intake port, and this means is linked to some control member which moves with engine speed, as a governor, or the throttle in the air intake pipe, This shutter means automatically opens'wider with increase of engine speed, and closes down as engine speed decreases. the flow of airv at slow engine speed, so that under such conditions the air is' Just enabled to reach the exhaust portjsimultaneously with closure of said port, and to allow freer flow of air, into the cylinder at higher speeds, so that the air is again enabled to reach the exhaust port'simultaneously with closure thereof. It will be Its effect is to restrict,

aria-sac evident that this feature of theinvention is applicable not only to the double opposed piston type of engine herein disclosed, but to two cycle engines in general, and the claims appended hereto are therefore not to be taken as limited to the double opposed type of engine except when expressly so restricted.

Further objects and features of the invention will appear from the following detailed descl'lvtion of a present preferred embodiment thereof,

reference for this purpose'being had to the accompanying drawings, in which:

Fig. 1 is a vertical transverse section throu h the cylinders of a twocylinder two cycle en i embodying my invention;

Fig. 2 is an end elevation ofthe engine shown in Fig. 1, parts being broken away;

Hg. 3 is a section taken as indicated by line 33,of Fig. 1;

. l"lg.4isaviewsimilartoFlg. 3butshowing modification;

Fig. 5 is a vertical section taken as indicated 1 6 is a detail perspective of a shutter memshown on the device of Pig..-4; and

l'ig.7'isatimingdiagramofthetwoupper -plstonsoftheengineofllg.'l.-

In the-drawings numeral l3 designates generally the-engine of the present invention, which embodies a housing ll, split medially on a horiaontalplane, the two halves being fastened to-' gether as at i2. Thecrank shaft ll of the engine extends longitudinally through the central portionof a crank chamber l3 defined by side walls II and upper and lower walls It and I1, respectively, provided by said housing, the center line C of the crank shaft being in the plane of split .of the housing, as shown. The upper and lower halves of housing H are provided, above and below crank chamber l3, with parallel, horizontally disposed cylinder bores 23 fitted with barrels 2|, each adapted to receive a pairof opposed pistons 22 and 23. These pistons may be provided with any suitable oil rings 23, and are arranged with their head ends toward one another, so as to define an intermediate combustion chamber. In the engine here shown, the charge between the two pistons is exploded by a spark from a spark plug 23 extending through barrel 2|, though any other manner of accomplishing combustion may be employed, if desired. The housing is shown provided with a suitable water jacket 26 surrounding cylinder bores 20.

Pistons 22 and 23 are provided with wrist pins 33, to which are pivotally connected rods 3| extending outwardly to pivotal connections with the outer extremities of rock levers 32, the latter being pivotally mounted at 33 on lugs 33 formed on the outer surfaces of housing side walls ii. To the inner ends ofrock levers 32 are pivotally connected rods which drive the crank shaft. In the preferred form of the engine here shown, the lower ends of the upper ro'ck levers are connected to the outer ends of rod 36, the inner ends of which are provided with straps 31 encircling 180! opposed crank pins and 39. Lower rock levers 32, on the other hand, have connected thereto rods-33a, the inner ends of which are pivotally connected at and H with lugs'l2 formed on the inner extremities of upper rods 36, as clearly shown. The upper pistons therefore drive the crank directly through rods 36, while the lower pistons drive the crank through rods It will be noted that the axial center line C of a the crank shaft lies below the arcs A described by the centers of the pivotal connections be- .tween upper rock levers 32 and rods 36, and above the corresponding arcs described by the pivotal connections 36a between lower rock levers 32 and rods 36a. This placement of the crank shaft relative to pivotal points 36 and 36a is essential to obtainment of the improved timing characteristic of the present invention, as will hereinafter be explained, and also affords improved leverage relations between the rock levers and the crank.

,The pistons 22 and 23 of each cylinder work oppositely to one another. For instance, considering the upper cylinder of the engine of Fig. 1, an explosion between the pistons causes them to be driven outwardly and to operate through the rock levers and connecting rods to rotate the crank shaft, one piston, as piston 23, driving one crank pin through an understroke while the other piston, as piston 23, drives the 180 opposed crank pin on an overstroke. The pistons of the other or lower cylinder are opposed by 180 degrees of crank shaft rotation to those of the upper cylinder, that is, are at inward dead center at the time the upper pistons are at outward dead center, and vice versa (see Fig. l). The

pistons of the lower cylinder are also so connected to the crank pins as to exert a torque on the crank shaft, one piston driving one crank pin on an overstroke while the other piston drives the opposed crank pin on an understroke. It will be evident that the power strokes of the upper and lower pairs of pistons are in 180 opposition, the crank shaft receiving power impulses alternately from the upper and lower pairs of pistons.

The explosive mixture or charge is conveyed to each cylinder by way of an intake manifold 66, and the exploded gases are removed through an exhaust manifold 6|. For the purpose of simplicity of explanation, the manifold and valve arrangements of only theupper cylinder will be described in detail, it being understood that exactly similar arrangements are provided for the lower cylinder. Intake manifold 66 communicates with an annular intake passage or chamber 63 formed in housing II and entirely surrounding piston barrel 2| (Figs. 1 and 3). This chamber 63 communicates with a series of intake ports 64 formed in barrel 2|, these ports being uniformly spaced about the barrel and placed just within the outer limit of movement of the head end of the corresponding piston 22, which may be referred to as the intake piston.

The intake passage is provided with an adjustable shutter device, here in the form of a ring or sleeve 66 rotatably mounted on barrel 2| within annular intake chamber 63, sleeve 66 thus being disposed entirely around intake ports 64.

This sleeve 66 is provided with a series of uniformly spaced apertures 61 corresponding to intake ports 64 (see Fig. 3). When sleeve 66 is in the position shown in- Fig. 3, its apertures 61 all register exactly with intake ports 64, so that a maximum freedom of air flow is obtained. It will be evident that rotation of sleeve 66 from the position shown in Fig. 3 will cause intake ports 64 to be gradually closed, thereby restricting the flow of air into the cylinder.

It will be noted that ports 64 and shutter apertures 61 are formed by slotting barrel 2| and sleeve 66 in directions offset to one side of the center line of the barrel. of causing the intake charge to be given a spiral motion in entering the barrel, which is conducive to uniformity of distribution of the charge. To further enhance this effect, I prefer to mount a series of baiiie members 69 on the sleeve, each of which extends outwardly from one side of a corresponding aperture 61, and' is disposed at such an angle as to prolong the spiral path which the charge is forced to take in entering the cylinder.

Rotation of sleeve 66 in either direction is accomplished through the medium of an arm 10 extending upwardly from chamber 63 into manifold 60, a link 'Il running longitudinally of manifold 60, and a rock lever 12 pivotally mounted in a wall of the manifold, the inner arm of said rock lever being pivotally connected at 13 to link H, and the other arm of the rock lever, which is outside the manifold, being connected to a link 14, operated as later to be described.

Connected to the manifold 60 of each of the upper and lower cylinders is an'intake pipe 6| leading from a supercharger 83, the latter being here indicated as of the positive displacement type. The specific supercharger here illustrated is of the gear type, comprising rotors 84 and 85, the former of which is keyed on the end of crank shaft H. A supercharger of the type here shown delivers a fixed quantity of air per crank shaft revolution, for a given intake pressure. However, while a supercharger of the positive displacement type is preferred, the well known blower or impeller type of supercharger may be utilized, though with some sacrifice in operating characteristics in certain cases. The carburetor I5 is here shown as placed ahead of the supercharger, being directly coupled to the supercharger intake pipe 16. The engine is throttled by means of a butterfly valve 11 between the carburetor and the supercharger, valve 11 being here shown as operated by swinging arm 18 moved by manually controlled link 19.

In the form of the invention here shown, throttle TI is interconnected with the rotatable shutter sleeves 66 surrounding the intake ports of the two cylinders. For this purpose, links 14 connected to the shutter operating rock levers 12 are connected at their inner ends to the two oppositely extending arms 96 and 9| of a rock lever 92, which is pivoted at 93 on any suitable support. Lever 92 is provided with a third arm 94, extending at right angles to arms 96 and 9|, to the end of which is pivotally connected one end of a link 95, the other end of which is connected to throttle operating arm I6, all as clearly shown in Fig. 2.

In the position shown in Figs. 2 and 3, throttl I1 is wide open, and shutter sleeves 66 are in such positions as to entirely uncover intake ports 64. It will be evident that movement of throttle arm 18 to close throttle 11 will rock lever 92 to move links 14 in an inward direction, thereby swinging rock levers I2 to cause rotation of shutter sleeve 66 and thereby gradually close intake This has the eflect ports 64. Thus intake ports 64 are opened and closed in accordance with opening and closing of the throttle valve, and are therefore closed down at low speed and opened up at high speed. The influence of this shutter action on operation of the engine will be further discussed at a later point in the specification.

The exhaust manifold 6| communicates with 'reached. At this time the charge is exploded, as

an annular chamber 22 entirely surrounding barrel 2| at the outer limit of movement of the head endofexhaustpiston22,aringofexhaustports llbeingformedinthewallofbarrelfl insucha position as to be Just insidethe head end of piston 22 when at said outermost position, these exhaust ports 21 opening within chamber 22, all as indicated in Fig. i.

The fresh charge is admitted to the cylinder through the intake port when the pistons are at the outer ends of their strokes, as they are in the upper cylinder in Fig. 1. This fresh charge advances in a column from the intake towards the exhaust port, which is also open, scavenging the cylinder of exploded gases.- The pistons then move inwardly. closing both the intake and exhaust ports, and compressing the fresh charge until their inward limits of movement are by a spark from plug 22, whereupon the pistons aredriven outwardly to complete the cycle.

The exact sequence of events characteristic of the engine of the present invention will be more fully understood from a consideration of the timing diagram of Fig. 7, in which the pistons, connecting rods, rock levers and crank shafts are shown in single line diagram, but are given the same identifying numerals as were applied to Fig. 1. This diagram illustrates only the upper cylinder and' its linkage connection with the crank shaft, sincethe timing characteristics of" the lower cylinder are substantially the same. In this diagram the crank pin circle is designated at P, and is divided into twenty-four equal parts, each representing 15 of crank pin rotation. The numerals on the outside of circle P represent successive 15' positions of crank pin 22, while the numerals on the inside of the circle represents successive 15 positions of the 180 opposed crank 50 Now if the longitudinal center line C of the crank shaft were so located as to intersect a line drawn tangentially to the arcsA described by the pivotal connections between rock levers 22 and rods 22, pistons 22 and 22 would reach and open the inlet and exhaust ports simultaneously, and likewise would cover said ports simultaneously as they returned from outward dead center. However, due to the downward offset of crank shaft center line C from said tangential line, the piston 22 linked to the crank pin 22 which is moving through its understroke as the pistons travel outwardlymoves with higher acceleration than does thepiston22linkedtothecrankpin2l which travels through its overstroke during outward movement of the piston. This will be readily apparent from inspection of the diagram of Fig. 7, exhaust piston 22 being shown to reach the exhaust port after 118 of crank shaft rotation from the full line position of the engine illustrated in the diagram, while intake piston 22 does not reach the intake port until the crank shaft has rotated through 142' from the same starting position.

' The exhaust port is therefore open 24' in advance of opening of the intake port. It will be evident from an inspection of Fig. 7 that this result is auasac due fact that the crank pin that moves through the under-stroke has a component of .motion away from its rock lever that is substantially greater than the component of motion of the other crank pin away from its rock lever during its corresponding overstroke. After opening of the intake port by intake piston 22, the exhaust piston continues to stay aheadof the intake piston, and recloses the exhaust port when the crank shaft has turned through an angle of 76 past the position at.which the intake port was opened, while the intake port is not closed by piston 22 until the crank shaft has turned through an additional angle of 24.

This sequence of events, and the extremely large advance of the exhaust piston over the intake piston, is of great advantage, as will now be explained. The exhaust piston 22 opens the exhaust port after 118' of'power stroke, and the exhaust gases and residuary flame immediately begin to escape through this port. Before the intake port opens, 24' later, all of the flame has passed out of the cylinder, so that upon open-- ing of the intake port and introduction of the fresh charge, there is no liability of backfiring.

The criterion is that suiilcient time should be allowed that the residuary flame will have passed out of the cylinder before the intake port opens, and it will be evident that the higher the speed of the engine, the greater must be the angular delay in'opening of the intake port. In the present engine, as previously stated, the intake port 'is not opened until 24 of crank shaft rotation after opening ofthe exhaust port. From my and it will be seen that the present engine meets this requirement.

The inertia of the exhaust gases rushing out through the exhaust ports causes the pressure in the cylinder to be finally depressed to some value below atmospheric. Upon opening of the intake port, the fresh charge, under supercharger pressure, then rushes in and advances through the cylinder, driving the remaining burnt gases before it and out of the cylinder by way of the exhaust ports. The rate of inlet of this fresh charge is so adjusted, in the manner hereinafter explained, that the fresh charge Just reaches the exhaust port at the time said port is closed by piston 22 in moving through its inward stroke. This closure of the exhaust port occurs 76 after opening of the intake port, thus affording a suitable scavenging period.

As previously noted, the intake port is open for 24 after the exhaust port is closed. This enables the supercharger 22 to raise the pressure of the mixture in the cylinder'to more than atmospheric before closure of the intake port and commencement of the compression stroke. I have found that-to enable proper supercharging in a high speed engine of the instant type the duration of this supercharging period should not be less than substantially 24 of crank shaft rotation, and it will be seen that the present en gine meets such requirement. After closure of the intake port by piston 22, the gases are compressed for 118 of crank shaft rotation, thus completing the cycle.

' It will be noted from Figs. 1 and 7 that the pivotal centers of rock levers 22 are offset inwardly from a straight line joining their piv- This is of advantage in that it improves the leverage relations between the rock levers and the crank. In particular, it decreases the angle between the lower arm of the rock lever and rod 36, so that said angle does not so nearly approach a straight angle in certain positions of the crank pin. This offset is sufllcient, in the embodiment here shown, that the angle between the lower arm of rock lever 32 and rod 38 at outward dead center (Fig. 7) is substantially equal to the supplement of the angle between said members at inward dead center. I may also, in some instances, increase the angle between the lower arm of lever 32 and rod 33 at outward dead center to a value greater than that shown, for instance, nearly or substantially to a right angle, while retaining the inward offset of centers 33, and thereby increase the effective lever arm of the rock lever (perpendicular distance between center 33 and rod 38) during the time piston pressure is the greatest.

- The leverage relations between the rock levers and the downwardly, or inwardly, offsetcrank shaft are also advantageous, in that the effective thrust at the crank pins increases with relatively great rapidity as the pistons move outwardly from inward dead center.

It has previously been described how the shutter ring 66 disposed about the intake port is automatically moved to open and close said port with increase and decrease of engine speed. The effect of this shutter action is as follows. It has previously been explained that the supercharger is of the positive displacement type, and it will be evident that the shutter device 63 will therefore not have an effect upon the quantity of air passing into the cylinder, but will affect the rate of flow into the cylinder during the time the intake port is open. At high engine speeds, the shutter is wide open, as in Fig. 3, and air flow into the cylinder is unrestricted by the shutter, and therefore moves through the cylinder to scavenge it of burnt gases with maximum velocity. At low engine speeds, on the other hand, the intake ports are partially covered by the shutter device, and air flow into the cylinder is restricted, with the result that additional time is required for the fresh air to travel the length of the cylinder. The relations of the various levers and links of the shutter and throttle controlmechanism is made such that in both cases, as well as at intermediate speeds, the shutter device establishes the rate of air flow into the cylinder at such a value that the fresh charge will just reach the exhaust port as said port is closed, thus assuring complete scavenging of the cylinder at all speeds of the engine, and also preventing partial loss of the fresh charge through the exhaust port at low engine speeds. The described air velocity control or shutter device of course has no effect upon the final quantity of air introduced to the cylinder, but does affect the rate at which the initial air enters the cylinder and travels to the exhaust port. It is desirable that the shutter device be located immediately adjacent the inlet ports opening into the cylinder, rather than at some point back in the intake manifold. for if the shutter were placed in the latter situation, .there' would be no control or restriction on entry into the cylinder, as the intake ports open, of that air between the shutter and the intake ports, which at low engine speed would tend to rush into and through the cylinder with undesirably high velocity.

A modified shutter mechanism is shown i i-Figs. 4, 5, andl. The intake manifold is indicated at "a, the annular intake chambersurrounding the.

barrel at 3a, the barrel at Ila, and the intake.

ports at a, Surrounding barrel 2la, within chamber 330, is a sleeve I III provided with'apertures 31a registering with ports a, as illustrated. This sleeve ill, while similar to the apertured sleeve 83 of the form of Fig. 3, is not rotatable on the barrel, being tightly fixed in the position shown in Fig. 4. Mounted on the outside of sleeve III are movable shutter members I ii adapted to open and close aperture "a. Said shutter members Ill, one of which is shown in perspective in Fig. 6, comprise shutter plates 2 hinged at one edge, as at H3, on pins Ill set into an outwardly extending annular flange ill on sleeve Ill. At the side edge of each plate 2 is a flange H0 provided with an annular slot Ill, and engaging in slots I" are pins 8 mounted in a ring member I23 surrounding and rotatable on one end of sleeve 0. This ring has an operating arm iii extending within manifold 30a. Movement of arm I causes ring I20 to rotate about sleeve 3, whereby pins H3 engaging in angular slots ill of shutter members Iii cause said members to swing in and out to control the inlet ports. As here shown, arm I is operated by means of a pin I2! engaging in a slot I26v in its upper end, said pin I" being mounted on a crank disc I21 on the inner end of "a shaft I28 iournalled in a bearing [28 mounted in a side wall of manifold "a, said bearing being suitably packed, as shown. The outer end of shaft I28 is indicated as operated by means of a lever arm ill, which may be understood to be operated in relation to engine speed in any desired manner. It will be evident that the shutter device in the form of Figs. 4, 5, and 6 accomplishes the same result as does the shutter device of Fig. 3.

It will be understood the drawings and description are to be considered merely as illustrative of and not restrictive on the broader claims appended hereto, since various changes in design, structure, and arrangement may be made without departing from the spirit and scope of said claims.

I claim:

1. An internal combustion engine comprising, a horizontally disposed cylinder, a pair of opposed pistons in said cylinder, a pair of rock levers, the upper ends of which are located outside opposite ends of the cylinder, and each connected at its upper end to the associated piston, a crank shaft extending below and at right angles to the axis of said cylinder, means pivotally mounting said rock levers to swing about fixed axes which are parallel to the axis of the crank shaft, rods pivotally connected to the lower ends of said rock I levers and to opposed pins of said crank shaft, the axis of said shaft lying below a line tangential to the arcs described by the pivotal connections between the rock levers and said rods, there being an intake port in the cylinder just within the outer limit of movement of one piston and an exhaust port in the cylinder just within the outer limit of movement of the other piston.

2. An internal combustion engine comprising, a horizontally disposed cylinder, a pair of opposed pistons in said cylinder, a pair of rock levers, the upper ends of which are located outside opposite ends of the cylinder, said levers having intermediate pivotal mountings on fixed axes extending at right angles to the axis of the cylinder, a link pivotally connected to the upper end of each rock lever and to the associated piston, a

crank shalt extending below and at right angles to the axis oi said cylinder, rods pivotally connected to the lower ends oi said rock levers and toopposedpinsoisaidcrankshaittheaxisoi said shaft lying below a line tangentialito the arcs described by the pivotal connections between the rock levers and said rods, the pivotal mounting axes of the two rocklevers being oilset to-' wards one another from straight lines joining their pivotal end connections, there being an intake port in the cylinder Just within the outer limit oi movem'ent oi one piston and an exhaust port in the cylinder just within the outer limit oi movement oi the other piston.

8. An internal combustion engine comprising,'a horlsontelly disposed cylinder, a pair of opposed pistons in said cylinder, a pair of rock levers, the upper ends oi which are located outside opposite ends of said cylinder, and each connected at its upperendtotheassoclatedplstonacrankshaft having opposed crank pins, said crank shaft beingrotatableinonedirectionin theengine and being disposed with its longitudinal axis below and at right angles to the axis of said cylinder, means pivotally mounting said rock levers to swing about ilxed axes which are parallel to the axis oi the crank shaft, rods pivotally connected to the lower ends of said rock levers and to the opposed pins of said crank shaft, the longitudinal axis of the crank shalt lying below a line tangential to the arcs described by the pivotal con,- nections between the rock levers and said rods, there being an intake'port opening within the cylinder at a point just within the outer limit of movement of that piston which is interconnected with the crank pin that moves through an overstroke during outward movement oi said piston, and an exhaust port leading from the cylinder from a point just within the outer limit of movement of that piston which is interconnected with the crank pin that moves through an understroke during outward movement 0! said piston.

4. An internal combustion engine comprising, a pair 01' vertically separated, parallel, horizontally disposedcylinderaapairoiopposedpistonsin each of said cylinders, a pair oi rock levers for each cylinder, each rock lever being pivoted on a ilxed axis, the outer ends oi. the rock levers being disposed outside opposite ends of their respective cylinders, and each being connected at its outer end to the associated piston, a crank shaltv having two 180 opposed crank pins, said shai't extending between and at rightangles to the two cylinders, rods pivotally connected to the inner ends oi said rock levers, straps encircling the two crank pins mounted on the inner ends otthercdsccnnectedtoonepairoirocklevers, pivotal connections between the inner ends of the otherrodsandthestrapendsoitheflrstrods,

the longitudinal axis of the crank shaft lying between lines drawn tangentially to the area deand at right angles to the two cylinders, a pair' of rock levers for each cylinder, each rock lever being pivoted on a fixed axis, the outer ends of the rock levers .being disposed outside opposite ends of their respective cylinderaand each being connected at its outer end to the associated piston, and rods pivotally connected between the inner ends of each pair of said rock levers 180' opposed pins 0! the crank shaft, the arcuate paths described by the pivotal connection points between the inner ends of each pair oi rock levers being so positioned that a line drawn tangentially to said arcuate paths lies between the longitudinal center line of the crank shatt and the associated cylinder.

'r c. comm. 

